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Chapter 4 Pp

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Defining the atom,structure of the atom, rutherfords gold foil experiment, distinguishing among atoms, mass number, atomic number, isotopes

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Chapter 4 Pp

  1. 1. Chapter 4: Atomic Structure
  2. 2. 4.1 Defining the Atom <ul><li>An Atom is the smallest particle of an element that retains its identity in a chemical reaction. </li></ul><ul><li>The Greek Philosopher </li></ul><ul><li>Democritus , was among the </li></ul><ul><li>First to suggest the existence </li></ul><ul><li>Of atoms. </li></ul>
  3. 3. <ul><li>Democritus believed that atoms were indivisible and indestructible. </li></ul><ul><li>Although Democritus’s ideas agreed with later scientific theory, they did not explain chemical behavior. </li></ul><ul><li>They also lacked experimental support. </li></ul>
  4. 4. Dalton’s Atomic Theory <ul><li>By experimental methods, Dalton transformed Democritus’s ideas on atoms into scientific theory. </li></ul><ul><li>Dalton studied the ratios in which elements combine in chemical reactions. Based on the results of his experiments, Dalton formulated hypotheses and theories to explain his observations. </li></ul>
  5. 5. Dalton’s Atomic Theory <ul><li>All elements are composed of tiny indivisible particles called atoms. </li></ul><ul><li>Atoms of the same element are identical. The atoms of any one element are different from those of any other element. </li></ul><ul><li>Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds. </li></ul><ul><li>Chemical reactions occur when atoms are separated, joined, or rearranged. </li></ul>
  6. 6. Sizing up the Atom…. <ul><li>Copper atoms are very small. </li></ul><ul><li>A copper coin the size of a penny contains about 2.4 x 10^22 atoms. By comparison, Earth’s population is only about 6 x 10^9 people. </li></ul><ul><li>If you could line up100,000,000 </li></ul><ul><li>Copper atoms side by side, they would produce a line only 1 cm long. </li></ul>
  7. 7. 4.2 Structure of the Nuclear Atom <ul><li>Much of Dalton’s atomic theory is accepted today. One important change however, is that atoms are now known to be divisible. </li></ul><ul><li>Three kinds of subatomic particles are electrons, protons, and neutrons. </li></ul>
  8. 8. Electrons <ul><li>In 1897, English physicist J.J. Thomson discovered the Electron. </li></ul><ul><li>Electrons are negatively charged subatomic particles. </li></ul><ul><li>Thomson called these particles corpuscles; later they were named electrons. </li></ul>
  9. 10. Robert A. Millikan (1868-1953) <ul><li>Carried out experiments to find the quantity of charge carried by an electron. </li></ul><ul><li>An electron carries exactly 1 negative charge and its mass is 1/1840 the mass of a hydrogen atom. </li></ul>
  10. 11. <ul><ul><ul><ul><ul><li>You need to understand…. </li></ul></ul></ul></ul></ul><ul><li>Atoms have NO CHARGE!! </li></ul><ul><ul><ul><ul><ul><li>They are electrically neutral. </li></ul></ul></ul></ul></ul>
  11. 12. <ul><li>Next…….. </li></ul><ul><li>Electric charges are carried by particles of matter. </li></ul>
  12. 13. Third…… <ul><li>There are NO fractions of charges, only whole number multiples!!! </li></ul>
  13. 14. And Finally……. <ul><li>When a negative particle combines with a positive particle an electrically neutral particle is formed. </li></ul><ul><li>+1 + -1 = 0 </li></ul>
  14. 15. Eugene Goldstein <ul><li>Observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. </li></ul><ul><li>He called these rays canal rays and concluded that they were composed of positive particles. </li></ul><ul><li>These positive particles are called Protons. </li></ul>
  15. 16. James Chadwick <ul><li>In 1932, an English Physicist confirmed the existence of yet another subatomic particle: The Neutron. </li></ul><ul><li>A neutron is a subatomic particle with no charge but with a mass nearly equal to that of a proton. </li></ul>
  16. 17. Plum Pudding Model <ul><li>In Thomson’s atomic model, known as the plum pudding model, electrons were stuck into a lump of positive charge, similar to raisins stuck in dough. </li></ul>
  17. 18. <ul><li>This model of the atom turned out to be short lived, however, due to the groundbreaking work of Ernest Rutherford (1871-1937), a former student of Thomson. </li></ul>
  18. 19. Rutherford’s Gold Foil Experiment
  19. 20. <ul><li>Rutherford’s Gold Foil Experiment </li></ul><ul><ul><ul><ul><ul><li>Here is a video of what happened!!! </li></ul></ul></ul></ul></ul>
  20. 21. Rutherford Atomic Model <ul><li>He proposed that the atom is mostly empty space , thus explaining the lack of deflection of most of the alpha particles . </li></ul><ul><li>He concluded that all the positive charge and almost all the mass are concentrated in a small region. </li></ul><ul><li>He called this region the Nucleus. </li></ul><ul><ul><ul><li>The nucleus is the tiny central core of an atom and is composed of protons and neutrons. </li></ul></ul></ul>
  21. 22. Key Concept <ul><li>In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom. </li></ul>
  22. 23. <ul><li>Although it was an improvement over Thomson’s model of the atom, Rutherford’s model turned out to be incomplete. </li></ul><ul><li>In Chapter 5, we will learn how it was revised. </li></ul>
  23. 24. 4.3 Distinguishing Among Atoms <ul><li>Elements are different because they contain different numbers of protons. </li></ul>
  24. 25. Atomic Number <ul><li>The atomic number of an element is the number of protons in the nucleus of an atom of that element. </li></ul>
  25. 26. Mass Number <ul><li>The total number of protons and neutrons in an atom is called the mass number. </li></ul><ul><li>Number of neutrons = mass number – atomic number </li></ul><ul><li>The number of neutrons in an atom is the difference between the mass number and atomic number. </li></ul>
  26. 27. <ul><li>If you know the atomic number and mass number of an atom of any element, you can determine the atom’s composition. </li></ul><ul><li>How do you calculate mass number? </li></ul>
  27. 28. Isotopes <ul><li>Isotopes are atoms that have the same number of protons but different numbers of neutrons. </li></ul><ul><li>Because isotopes of an element have different numbers of neutrons, they have different mass numbers. </li></ul>
  28. 29. Isotopes Cont… <ul><li>Atomic mass unit is defined as one twelfth of the mass of a carbon-12 atom. </li></ul><ul><li>In nature most elements occur as a mixture of two or more isotopes. </li></ul><ul><li>Isotopes of an element has a fixed mass and a natural percent abundance. </li></ul>
  29. 30. Relative Abundance <ul><li>The Atomic Mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element. </li></ul><ul><li>A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature. </li></ul>
  30. 31. Determine Atomic Mass <ul><li># stable isotopes </li></ul><ul><li>Mass of each isotope </li></ul><ul><li>Natural % abundance of each isotope </li></ul><ul><li>Atomic Mass = Mass of Isotope x natural abundance = add them together </li></ul><ul><li>Look on page 117 for practice problems!! </li></ul>
  31. 32. The Periodic Table – A Preview <ul><li>Each horizontal row of the periodic table is called a PERIOD. </li></ul>
  32. 33. Periodic Table Cont…. <ul><li>Each vertical column of the periodic table is called a group. </li></ul><ul><li>Elements within a group have similar chemical and physical properties. </li></ul>
  33. 34. Lets Review!!! <ul><li>Atoms are the smallest particle of an element that retains its identity in a chemical reaction. </li></ul><ul><li>Democritus believed that atoms were indivisible and indestructible. </li></ul><ul><li>Dalton’s atomic theory states that </li></ul><ul><ul><li>All elements are composed of atoms </li></ul></ul><ul><ul><li>Atoms of different elements combine to form compounds </li></ul></ul><ul><ul><li>Atoms of the same element are identical </li></ul></ul><ul><ul><li>Chemical reactions occur when atoms are separated, joined, or rearranged. </li></ul></ul>
  34. 35. Review Cont…. <ul><li>There are 3 subatomic particles </li></ul><ul><ul><li>Proton </li></ul></ul><ul><ul><li>Identifies the atom </li></ul></ul><ul><ul><li>Positive charge </li></ul></ul><ul><ul><li>Electron </li></ul></ul><ul><ul><li>Determines chemical reactions </li></ul></ul><ul><ul><li>Negative Charge </li></ul></ul><ul><ul><li>Neutron </li></ul></ul><ul><ul><li>Determines Isotope </li></ul></ul><ul><ul><li>Neutral Charge </li></ul></ul>
  35. 36. Review Cont… <ul><li>Thomson atomic model, known as the plum pudding model, electrons were stuck into a lump of positive charge. </li></ul><ul><li>Rutherford’s Gold Foil Experiment: He proposed that atoms are mostly empty space. </li></ul><ul><li>The nucleus is the tiny central core of an atom made of protons and neutrons. Electrons surround the nucleus. </li></ul><ul><li>Atomic number is the number of protons. </li></ul><ul><li>Mass number is the # of protons and neutrons. </li></ul><ul><li>Isotopes are atoms that have the same number of protons but a different number of neutrons. </li></ul>
  36. 37. Review Cont… <ul><li>Atomic mass unit is defined as one twelfth of the mass of a carbon-12 atom. </li></ul><ul><li>The atomic mass of an element is the weighted average mass of the atoms in a naturally occurring sample of the element. </li></ul><ul><li>To calculate the atomic mass of an element, multiply the mass by its natural abundance and then add the products. </li></ul>
  37. 38. Review Cont… <ul><li>Periodic Table allows you to easily compare the properties of one element to another element. </li></ul><ul><li>Groups go down!! </li></ul><ul><li>Periods all across!! </li></ul><ul><li>Elements within a group has similar physical and chemical properties. </li></ul>

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